Screw-type compressor having an axial bearing part on only one rotor

ABSTRACT

A screw-type compressor comprises a housing ( 12 ) in which a primary rotor ( 14 ) and a secondary rotor ( 16 ) are arranged each of which is provided with a shaft ( 18,24 ) and a screw rotor ( 20,26 ). The secondary rotor ( 16 ) is axially supported by the primary rotor ( 14 ). Only the primary rotor ( 14 ) comprises an axial bearing part ( 22 ) which is supported in an axial bearing part ( 66 ) of the housing ( 12 ). The omission of an axial bearing between the secondary rotor and the housing simplifies the support of the secondary rotor.

BACKGROUND OF THE INVENTION

The invention relates to a screw-type compressor comprising a housing inwhich are arranged a primary rotor and a secondary rotor each having ashaft and a screw rotor.

Screw-type compressors are used for compressing a gaseous substance, e.g. air, and making it available as compressed gas. From DE-A-42 27 332 ascrew-type compressor is known wherein a motor-driven primary rotordrives a secondary rotor. The shafts of the primary and secondary rotorsare radially supported in roller bearings at both ends. Further, eachshaft of the two rotors is axially supported in a plurality of ballbearings at one end. Said axial bearings carry the forces, which occurbetween the screw rotors during gas compression, in axial direction ofthe primary and the secondary rotor. The antifriction bearings produceheat during operation, which leads to inhomogeneous heat distributionand thus to stresses in the shaft. From DD-PS 84 891 and U.S. Pat. No.3,811,805 compressors are known whose primary and secondary rotors areeach provided with axial bearings which are configured as slide bearingand thus produce less heat. U.S. Pat. No. 3,275,226 describes ascrew-type compressor wherein the primary and secondary rotors areaxially supported by antifriction bearings with the primary rotor beingadditionally axially supported by a disk. The multitude of bearings forthe primary and the secondary rotor render the configurations of theknown screw-type compressors complicated and their manufactureexpensive.

SUMMARY OF THE INVENTION

It is the object of the invention to simplify and improve support of theprimary and the secondary rotors in a screw-type compressor.

In the screw-type compressor according to the invention the secondaryrotor is axially supported by the primary rotor. Only the primary rotorcomprises an axial bearing part which is supported in an axial bearingpart of the housing. The secondary rotor is thus directly supported bythe housing only via radial bearings. The secondary rotor however is nolonger directly supported by the housing via its own axial bearing. Theaxial forces of the secondary rotor are transmitted via its screw rotorto the screw rotor of the primary rotor. The axial bearing of theprimary rotor, formed by the axial bearing parts of the primary rotorand the housing, thus takes up all axial forces of the primary rotor andthe secondary rotor.

By omission of the axial bearing between secondary rotor and housing theoverall complexity with regard to support of the primary and thesecondary rotor is reduced by at least one (axial) bearing.

An axial bearing supported by the housing is provided only for theprimary rotor with the majority of the axial forces occurring during gascompression acting upon said bearing. The secondary rotor, upon whichacts a considerably less amount of the axial forces produced during gascompression, is supported via the tooth flanks of its screw rotor at thescrew rotor of the primary rotor.

The primary rotor is provided with the only axial bearing since largeraxial forces act upon the primary rotor than on the secondary rotor. Inthis configuration only the relatively low axial forces of the secondaryrotor need to be transmitted via the screw rotor teeth onto the primaryrotor. Generally the secondary rotor may also be axially supported viaan axial bearing at the housing while the primary rotor is axiallysupported via the screw rotors at the secondary rotor and thus does notcomprise its own axial bearing connected with the housing.

In a preferred embodiment the axial bearing formed by the axial bearingparts is configured as slide bearing. The radial bearings, too, may beexecuted as slide bearings. The configuration of the axial slide bearingis simpler than that of an antifriction bearing and thus facilitateslow-cost manufacture of the screw-type compressor. Slide bearingsfurther present the advantage that they do not produce any appreciableheat so that the rotor shafts remain stressfree even at high speeds. Theslide bearing may be lubricated with the same medium which is also usedas lubricating and sealing agent in the compression chamber of thescrew-type compressor. Oil or water may serve as gliding, lubricatingand sealing fluid. However, air may also be used as slide bearing fluid.

When the primary rotor is belt-driven, an antifriction bearing ispreferably used as radial bearing on the drive side since slide bearingsare not suited for accommodating extremely high radial stresses.

In a preferred embodiment axial thrust forces of the secondary rotor areaxially countered by the primary rotor exclusively via the front endfaces of the meshing teeth of the screw rotors bearing against a bearingdisk. The teeth of the screw rotors may be configured such that onlyvery low axial forces or none at all occur on the secondary rotor sothat these low axial thrust forces of the secondary rotor can withoutany problems be transmitted via the secondary screw rotor teeth to theprimary rotor. A further means for transmitting the axial forces fromthe secondary rotor to the primary rotor is not required.

The secondary rotor preferably comprises an axial tensioning means whichaxially biases the secondary rotor. The axial tensioning means is notprovided with a stop which could support the secondary rotor but appliesa constant biasing force to the secondary rotor, preferably thesecondary rotor shaft, the biasing force substantially corresponding tothe anticipated axial stress acting on the secondary rotor during gascompression. The tensioning means thus substantially compensates for theaxial forces acting upon the secondary rotor so that only very low axialforces or none at all have to be transmitted from the secondary rotor tothe primary rotor. In a preferred embodiment the axial tensioning meansis configured as a hydraulic tensioning means acting upon the shaft orthe screw rotor of the secondary rotor. The tensioning means may also besupplied with air.

The axial bearing part of the primary rotor is preferably arranged onthe screw rotor of the primary rotor. It is not the shaft of the primaryrotor but the screw rotor of the primary rotor which is supported by thehousing. The screw rotor, at which occur the axial forces produced bypressure generation as well as those transmitted by the secondary rotor,is directly supported by the housing which takes up the axial forceswithout any transmission via another component. Thus the primary rotordoes not apply any axial stresses to the shaft so that the shaft isloaded to a smaller degree by corresponding torques and shearing forces.

In a preferred embodiment the axial bearing part of the primary rotor isconfigured as an axial front wall of the screw rotor. The axial bearingpart of the housing is executed as an annular disk-shaped running facewith the two axial bearing parts together forming the slide bearing. Thefront wall of the primary rotor screw rotor thus forms a bearing facesupported on the ring-shaped running face of the housing. In thisconfiguration no bearing-specific parts must be provided on the primaryrotor. This renders manufacture of the primary rotor less expensive.

In an alternative embodiment the primary rotor comprises a slide bearingdisk on an axial front end face of the screw rotor, which forms,together with an axial bearing part running face of the housing, theslide bearing.

On a front end face of the rotor of the primary rotor a ring-shapedslide bearing disk is provided which forms a closed radial runningsurface.

The screw rotor front wall or the slide bearing disk preferablycomprises substantially radial grooves for a gliding fluid. The glidingfluid, which is introduced near the shaft or at the basis of the screwrotor, can be fed by the centripetal forces via said grooves to theoutside. In this way a gliding film is produced over the overall radiusand circumference of the screw rotor.

In a preferred embodiment the grooves take an arcuate path with theouter end of each groove, as seen in radial direction, being curved in adirection opposite to the sense of rotation of the rotor. This resultsin very uniform gliding fluid distributions over the overall radius andcircumference of the screw rotor.

The grooves are preferably T-shaped with the vertical part beingarranged radially and the horizontal part being arranged tangentially incircumferential direction. The T-shaped grooves allow good lubricationof the slide bearing in both running directions of the primary rotor.

In a preferred embodiment a front end face of the secondary rotor screwrotor is axially supported on the slide bearing disk of the primaryrotor. The front faces of the rotor teeth of the secondary rotor abutthe rotorside end of the slide bearing disk. Thus an axial support ofthe secondary rotor is realized by simple means so that even largeraxial forces can be transmitted.

In a preferred embodiment the screw rotor, the shaft and the slidebearing disk of the primary rotor are integrally formed. The primaryrotor may be manufactured from a composite material by casting,injection molding etc. in a negative mold.

Alternatively the slide bearing disk may be separately configured andcast, bolted or in any other way fastened to the shaft and/or the screwrotor of the primary rotor. In the case of separate manufacture of theslide bearing disk and the primary rotor different materials may beselected for shaft, rotor and slide bearing disk, which can be betteradapted to the respective physical requirements of the respectivecomponent. The screw rotor may, for example, be milled from a compositematerial in a conventional manner and the metal slide bearing disk maysubsequently be bolted to the screw rotor.

According to a preferred embodiment a special radial bearing runninglayer is applied to the shaft of the primary or the secondary rotor. Theprimary rotor may, for example, be manufactured integrally, andsubsequently a super-gliding agent for the radial bearing may be appliedto the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereunder embodiments of the invention are explained in detail withreference to the drawings in which:

FIG. 1 shows a screw-type compressor comprising a primary rotor havingan axial slide bearing, and a secondary rotor axially supported by theprimary rotor,

FIG. 2 shows a first embodiment of the axial bearing parts of theprimary rotor,

FIG. 3 shows a second embodiment of an axial bearing part of the primaryrotor,

FIG. 4 shows a third embodiment of an axial bearing part of the primaryrotor,

FIG. 5 shows a first embodiment of a primary rotor with a separate slidebearing disk,

FIG. 6 shows the primary rotor and the mounted slide bearing disk ofFIG. 5,

FIG. 7 shows a second embodiment of the integral primary rotor, and

FIG. 8 shows a third embodiment of a primary rotor to whose shaft aradial bearing running layer is applied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a screw-type compressor 10 which serves for generation ofan oilfree compressed gas, e. g. air. The screw-type compressor 10comprises a housing 12 in which a primary rotor 14 and a secondary rotor16 are arranged axially parallel to each other. The primary rotor 14substantially comprises a shaft 18, a screw rotor 20 and a slide bearingdisk 22 which serves as axial bearing part of the primary rotor 14. Thesecondary rotor 16 is substantially provided with a shaft 24 and thescrew rotor 26. Both the shaft 24 and the screw rotor 26 of thesecondary rotor have a smaller diameter than the shaft 18 and the screwrotor 20 of the primary rotor 14. Both the primary rotor 14 and thesecondary rotor 16 are manufactured integrally from a compositematerial.

The primary rotor 14 can be driven via a shaft stub 28 which extendsfrom the housing 12. The drive is preferably carried directly via anelectric motor which is axially aligned with the longitudinal axis ofthe primary rotor.

To take up the radial forces acting upon the primary rotor 14 theprimary rotor shaft 18 is supported via two radial bearings 30,32 in thehousing 12. The secondary rotor 16, too, is supported via two radialbearings 34,36 in the housing 12. All radial bearings 30,32,34,36 areconfigured as slide bearings. The space enclosed by the housing 12, inwhich the primary rotor screw rotor 20 and the secondary rotor screwrotor 26 are arranged, forms the compression chamber 27 of thescrew-type compressor 10 where the gas is compressed. The housing 12comprises a gas opening, which is not shown, on the shaft stud 28 sidethrough which the gas to be compressed can flow into the compressionchamber 27. In the chambers formed by the teeth 21,25 of the screwrotors 20,26, i. e. the compression chamber 27, the gas is compressedand discharged in compressed form at the opposite axial end of thecompression chamber 27 via an opening in the housing, which is notshown. This discharge side of the screw-type compressor or the primaryand secondary rotors 14,16 is referred to as delivery side.

The radial bearings 30,32 and 36 have generally the same configuration.Via a gliding fluid inlet 38,39,41 a gliding fluid, i. e. water, flowsinto an annular groove 44. On each shaft 18, 24 a bearing bush 46, whichis surrounded by an annular groove 44, is seated which comprises threeradial bores 48 through which the gliding fluid can flow onto the outercircumference of the respective shaft 18, 24.

On the two delivery-side radial bearings 32,36 the gliding fluid isaxially distributed along the shaft 18,24 with the gliding fluid flowingtowards the compression chamber 27 being fed via an annular groove 50and collecting ducts 52,54 into a gliding fluid collecting chamber 57.Via two bores 56,58 the gliding fluid is injected into the compressionchamber 27.

In the drive-side radial bearing 30 of the primary rotor 14 the glidingfluid flows along the bearing bush 46 in both axial directions, i. e.towards a gliding fluid discharge 60 and towards the slide bearing disk22.

In the the secondary rotor 16 radial bearing 34 averted from thedelivery side the gliding fluid flows through an axial shaft bore 62 andthree radial bores 64 of the shaft 24, which are arranged relative toeach other at an angle of 120°, to the shaft circumference or thebearing bush 47. From there the gliding fluid flows on the shaftcircumference towards the compression chamber 27.

The primary rotor 14 comprises an axial bearing 15 which is configuredas a slide bearing. One axial bearing part of the axial bearing 15 isformed by the slide bearing disk 22 arranged at a front end face 88 ofthe screw rotor 20 and terminating the latter in axial direction. Theother axial bearing part is formed by an annular disk-shaped runningface 66 of the housing 12. The annular disk-shaped running faces 68,66of the slide bearing disk 22 and the housing 12, respectively, togetherform a slide bearing which supports the screw rotor 20 of the primaryrotor 18 directly at the housing 12.

The gliding fluid for the axial bearing 15 is fed via an intake 70 of anannular groove 72 to the primary rotor shaft 18 which axially extends upto the slide bearing disk 22. The gliding fluid is supplied at apressure of approximately 10 bar which substantially corresponds to thecompressed gas pressure.

According to FIG. 2 the slide bearing disk 22 comprises a plurality ofgrooves 23 which radially extend to the outside in an arcuate manner andtaper to a point, through which the gliding fluid is fed to the outsideby the centripetal forces occurring during rotation of the primary rotor14.

The gliding fluid leaves the grooves 23 of the slide bearing disk 22 andforms a fluid film between the running faces 66,68 of the housing 12 andthe axial bearing 15, respectively, which ensures sliding support. Thegliding fluid continues to flow to the outside and finally enters thecompression chamber 27.

The teeth 25 of the screw rotor 26 of the secondary rotor 16 mesh withthe teeth 21 of the screw rotor 20 of the primary rotor 14. Via thetooth flanks of the teeth 21 and 25 axial forces of the secondary rotor16 are transmitted to the teeth 21 of the primary rotor 14.

In the area of the front end face 74 of the shaft 24 of the secondaryrotor 16 a fluid chamber 76 is enclosed by a cover 78 of the housing 12,into which the gliding fluid for the radial bearing 34 is fed via theintake 40. The gliding fluid acts as a fluid pressure of approximately10 bar on the front end face 74 of the shaft 24 thus applying a force inaxial direction to the secondary rotor 16, which counteracts the axialforce produced during gas pressure generation and acting upon thesecondary rotor 16. This configuration thus acts as a fluidic orpneumatic axial tensioning means 80 which axially cushions the secondaryrotor 16 but does not comprise any stop for fixing the secondary rotor16 in a given axial position.

Besides the axial tensioning means 80 and the axial support of thesecondary rotor via the screw rotors 20,26 the secondary rotor isfurther supported by the rear side 82 of the slide bearing disk 22 whichsupports front end faces 83 of the teeth 25 of the secondary rotor screwrotor 26.

FIG. 3 shows a second embodiment of a slide bearing disk 22′ where theT-shaped gliding fluid grooves 84 are arranged. The vertical groove 85is radially arranged and the horizontal groove is tangentially arranged.In this configuration of the grooves 84 the primary rotor 14′ can beoperated in both senses of rotation with adequate lubrication beingensured in both senses of rotation.

FIG. 4 shows another embodiment of the primary rotor 14″ wherein noslide bearing disk is provided but the front end face 88 of the teeth 25serve as slide bearing face. For better distribution of the glidingfluid arcuate grooves 89 are arranged in the front end face 88.

In FIG. 5 a primary rotor 90 is shown which substantially comprises twoparts: the shaft 92 which is manufactured integrally with the screwrotor 94, e. g. from a composite or a metallic material, and the slidebearing disk 22′ which is manufactured from a material with good slidingproperties. The slide bearing disk 22′ is provided with four axialdriving lugs 95 which fit into mating bores of the screw rotor 94.

As shown in FIG. 6 the slide bearing disk 22′ is pushed onto the shaft92 and the driving lugs 95 are inserted into the mating openings of thescrew rotor 94. The slide bearing disk 22′ is then bolted to the screwrotor 94.

Alternatively the slide bearing disk can be manufactured separately andsubsequently be cast integral with the primary rotor 90 when the latteris cast.

FIG. 7 shows the primary rotor 14 of FIG. 1.

In FIG. 8 a primary rotor is shown wherein a radial bearing runninglayer 102 is applied to the shaft 18 on both sides of the screw rotor26, which presents better gliding properties than the shaft material andmay be manufactured from so-called super-gliding materials.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined the appended claims.

What is claimed is:
 1. A screw-type compressor comprising a housing(12), said housing defining a compression chamber (27); a primary rotor(14) having a primary shaft (18) and a primary screw rotor (20), asecondary rotor (16) having a secondary shaft (24) and a secondary screwrotor (26), said primary screw rotor (20) and said secondary screw rotor(26) being in meshed relationship in said compression chamber (27),means supporting said shafts (18, 20) for rotation, said primary screwrotor (20) and said secondary screw rotor (26) each having a respectivefront face (88, 83), a thrust bearing (15) located between said primaryscrew rotor front end face (88) and an axially opposing face (66) ofsaid housing (12) for countering axial thrust forces generated uponrotation of said screw rotors (20, 26), and said secondary screw rotorfront end face (83) being in axial opposing contact with said thrustbearing (15) to thereby counter axial thrust forces of said secondaryscrew rotor (26).
 2. The screw-type compressor as defined in claim 1wherein said thrust bearing (15) is a radial bearing.
 3. The screw-typecompressor as defined in claim 1 wherein said primary screw rotor (20)and said secondary screw rotor (26) have respective meshing teeth (21,25), and said secondary screw rotor front end face (83) is at least inpart defined by said secondary screw rotor teeth (25).
 4. The screw-typecompressor as defined in claim 1 wherein said compression chamber (27)includes a fluid suction side and a fluid discharge side, and means (80)for imparting axial forces to said secondary rotor (16) in a directiontoward said fluid discharge side.
 5. The screw-type compressor asdefined in claim 1 wherein said compression chamber (27) includes afluid suction side and a fluid discharge side, and means (80) forimparting fluidic axial forces to said secondary rotor (16) in adirection toward said fluid discharge side.
 6. The screw-type compressoras defined in claim 1 wherein said thrust bearing part (15) is inexternal telescopic relationship to said primary shaft (18).
 7. Thescrew-type compressor as defined in claim 1 wherein said secondary screwrotor front end face (83) defines a running surface in relation to saidthrust bearing part (15).
 8. The screw-type compressor as defined inclaim 1 wherein the primary shaft (18) and the slide bearing disk (22)are integrally formed.
 9. The screw-type compressor as defined in claim1 wherein the slide bearing disk (22′) is connected to one of theprimary shaft (18) and the primary screw rotor (20).
 10. The screw-typecompressor as defined in claim 1 wherein radial bearings (102) areapplied to at least one of the primary shaft (18) and the secondaryshaft (24).
 11. The screw-type compressor as defined in claim 1 whereinthe secondary screw rotor (26) includes teeth (25), axial end faces ofsaid teeth (25) are defined by said secondary screw rotor front end face(83), and said secondary screw rotor teeth end faces are in axialopposing contact with said thrust bearing (15).
 12. The screw-typecompressor as defined in claim 1 wherein said thrust bearing (15) is aslide bearing.
 13. The screw-type compressor as defined in claim 12wherein the axial support of the secondary rotor (16) provided by theprimary rotor (14) is provided exclusively via the meshing teeth (21,25) of the screw rotors (20, 26).
 14. The screw-type compressor asdefined in claim 1 wherein said primary screw wall front end face (88)and the slide bearing disk (22) include substantially radial grooves(23, 89) for gliding fluid.
 15. The screw-type compressor as defined inclaim 14 wherein the substantially radial grooves (23, 89) define anarcuate path.
 16. The screw-type compressor as defined in claim 14wherein the substantially radial grooves (84) are T-shaped.